1. Field of the Invention
The invention relates to an image forming apparatus such as a copier or a laser printer and further, a detecting device for detecting the type and thickness of a sheet.
2. Description of the Related Art
An image forming apparatus such as a copier or a laser printer is provided with a latent image bearing member for bearing a latent image thereon, a developing device for imparting a developer to the latent image bearing member to thereby visualize the latent image as a developed image, transferring means for transferring the developed image developed by the developing device to a recording material transported in a predetermined direction, and a fixing device for heating and pressurizing the recording material to which the developed image has been transferred by the transferring means under a predetermined fixing process condition to thereby fix the developed image on the recording material.
In such an image forming apparatus, for example, the size or type of a recording sheet which is used as a recording material (hereinafter referred to also as the sheet type) is set on an operating panel provided in the main body of the image forming apparatus by a user, and control is done so as to set a fixing process condition (for example, the fixing temperature or the transporting speed of the recording sheet passing the fixing device) in conformity with the setting.
Also, when the recording sheet is an OHT sheet, whether the recording sheet is an OHT sheet or not is automatically detected by a transmission sensor provided in the interior of the image forming apparatus, and if light is transmitted through the recording sheet, it is judged to be an OHT sheet, and if light is not transmitted through the recording sheet, it is judged to be plain paper, and control is done so as to set the fixing temperature or the transporting speed of the recording sheet in conformity with the result of the judgement.
However, the above-described conventional image forming apparatus has suffered from the following problems:
(1) It is necessary for the user to effect the setting of the sheet type in the image forming apparatus or PC and therefore, the image forming apparatus is inferior in its operability. Particularly, the user""s load is great and the usability of the apparatus is bad.
(2) In recent years, the number of sheet types handled has become great and the set performed in advance cannot cover all sheet types. As the a result, the setting of the fixing process condition is not determined well and the fixing property becomes bad. Particularly, in the case of rough paper of which the surface paper fiber is asperate, the fixing becomes bad unless the toner on the recording sheet is sufficiently fusion-bonded.
(3) For example, by recording sheets being left stacked for a long time or left in the atmosphere for a long time, the surface roughness or the state of the surface paper fiber of the recording sheets may be changed. In such case, even if the sheet type is set by the set mode and the fixing process condition is set, it does not always coincide with the condition of recording sheets actually used and the fixing becomes bad.
(4) When the fixing process is effected on a recording sheet of such a type that the surface paper fiber of the recording sheet has been compressed with the fixing temperature set to a high level, the fusion bond of the toner occurs more than necessary and the gloss becomes higher than necessary and the quality of image becomes lower and besides, the electric power of the fixing device is consumed more than necessary, and this is not economical.
(5) The transmission sensor for the automatic detection of OHT sheets cannot judge the other sheet types and becomes a sensor exclusively for OHT, and the cost performance of the system total cost of the apparatus is bad.
(6) There are various methods of detecting the type of a recording sheet such as thick paper, but in both of (i) a method using, for example, a reflection sensor and (ii) a method of mechanically detecting the thickness of paper, a sensor exclusively for detecting the thickness of paper becomes necessary, and the cost performance of the system total cost of the image forming apparatus is bad.
So, it is an object of the present invention to provide an image forming apparatus which achieves improvements in usability and cost performance and yet can effect the fixing process for recording materials of various types under an optimum fixing process condition to thereby obtain good fixed images.
It is another object of the present invention to provide an image forming apparatus comprising:
feeding means for feeding a sheet;
image forming means for forming an image on the sheet fed by the feeding means;
recording means for reading a picture of the surface of the sheet fed by the feeding means;
discriminating means for discriminating whether rereading is necessary, on the basis of the picture read by the reading means;
means for changing the reading condition of the reading means and causing the picture of the edge portion of the sheet to be read again, on the basis of the fact that it has been discriminated by the discriminating means that rereading is necessary;
detecting means for detecting the type of the sheet on the basis of the picture read by the reading means; and
control means for controlling the image forming condition of the image forming means on the basis of the result of the detection by the detecting means.
It is another object of the present invention to provide a detecting device comprising:
reading means for reading a picture of the surface of a fed sheet;
discriminating means for discriminating whether rereading is necessary, on the basis of the picture read by the reading means;
means for changing the reading condition of the reading means and causing the picture of the edge portion of the sheet to be read again, on the basis of the fact that it has been discriminated by the discriminating means that rereading is necessary; and
detecting means for detecting the type of the sheet on the basis of the picture read by the reading means.
It is another object of the present invention to provide an image forming apparatus comprising:
feeding means for feeding a sheet;
image forming means for forming an image on the sheet fed by the feeding means;
reading means for reading a picture of the edge portion of the sheet fed by the feeding means;
detecting means for detecting the thickness of the sheet on the basis of the picture read by the reading means; and
control means for controlling the image forming condition of the image forming means on the basis of the result of the detection.
It is another object of the present invention to provide a detecting device comprising:
reading means for reading a picture of the edge portion of a fed sheet; and
detecting means for detecting the thickness of the sheet on the basis of the picture read by the reading means.
Other objects, constructions and effects of the present invention will become apparent from the following detailed description and the accompanying drawings.